Flame retardant polymers

ABSTRACT

Polyolefins based on propylene are made flame retardant by the addition of about 0.1 to 2 percent by weight of a dialkyltin mercaptoester and 0.1 to 2 percent by weight of an aromaticaliphatic ether having at least one bromophenoxy linkage to an aliphatic radical and having at least three bromine substituents on each aromatic ring.

United States Patent 1 1 Kutner [541 FLAME RETARDANT POLYMERS [75] Inventor: Abraham Kutner, Wilmington, Del.

[73] Assignee: Hercules Incorporated, Wilmington,

Del.

22 Filed: May 6, 1971 21 App]. No.: 140,949

[52] 11.8. C1. ..260/45.75 K, 260/4595 G [51] Int. Cl. ..C08t 45/62 [58] Field of Search ..260/45.75 X, 45.95, 613

[56] References Cited UNITED STATES PATENTS 3,075,944 1/1963 Wick et a1. ..260/41 3,250,739 5/1969 Sauer et a1 ..260/45.75 3,400,174 9/1968 l-leidel et al.' ..260/612 1 51 Feb. 20, 1973 3,372,141 3/1968 Dickerson et al. ..260/45.95 3,368,916 2/1968 Hattori ....260/45.75 3,282,882 11/1966 Vuillemenot et a1. ..260/612 3,666,692 5/1972 Paige et al. ..260/2.5

Primary Examiner--Donald E. Czaja Assistant ExaminerV. P. Hoke Attorney--Edwin H. Dafter, Jr.

'[57] ABSTRACT 3 Claims, No Drawings FLAME RETARDANT POLYMERS This invention relates to flame retardant compositions based on stereoregular polymers of propylene.

In recent years, polypropylene and, in many cases, other polyolefins as well, have become recognized as having considerable potential utility as molded components in the automotive field, in appliance manufacture, and in the electrical industry. Additionally, fibers and yarns of polypropylene are becoming increasingly popular in carpeting and upholstery applications. In view of the nature of the applications in which this polymer is usually employed, good flame resistance and flame retardancy are imperative.

Considerable research effort has been extended toward the goal of improving the flame resistance of the polyolefins. While a fair degree of success has been realized, it has frequently been at the expense of other properties of the polymers. To be acceptable in commercial formulations, flame retardancy additives must be effective at low concentrations, must be stable at polymer processing temperatures and must not contribute excessively to polymer degradation at processing temperatures. Representative patents showing the state of the polyolefln flameproofmg art include U.S. Pats. Nos. 3,075,944; 3,158,588; 3,368,916; 3,418,263; 3,419,518 and 3,432,461.

U.S. Pat. No. 3,075,944 teaches to incorporate to 20 percent by weight of a 2,4,6-tribromoaniline derivative or 5 to 20 percent by weight of an halogenated diaromatic or aromatic-aliphatic ether having at least three halogen atoms attached to an aromatic group and 3 to percent by weight of antimony trioxide. Thus, a minimum of 8 percent of the additive combination is required.

U.S. Pat. No. 3,158,888 teaches the incorporation of about 10 to 50 percent by weight of hexachlorodicylopentadiene and about 1 to 30 percent by weight of antimony oxide into a polyolefin.

U.S. Pat. No. 3,368,916 teaches incorporation of about 4 to 8% by weight of a bromine containing compound such as an ester of 2,3-dibromopropanol and phosphoric acid, and 0.2 to 1 percent of an organotin heat stabilizer into polystyrene and coating the surface of an article. produced therefrom with an acrylic polymer.

U.S. Pat. No. 3,418,263 teaches the incorporation into a polyolefin of about 2 to 50 percent by weight of a halogenated cyclopentadiene Diels-Alder adduct, 1 to 30 percent by weight of antimony, arsenic, or bismuth oxide, and 0.1 to 3 percent by weight of a color stabilizer.

U.S. Pat. No. 3,419,518 teaches the incorporation of about 0.2 to 10 percent by weight of antimony trioxide and l to 1.3 percent of an aliphatic organic compound containing 45 to 93 percent bromine into polypropylene. Cycloalkanes are preferred brominated compounds.

U.S. Pat. No. 3,432,461 teaches the incorporation into a polymer of about 1 to 95 weight percent of ar-- senic, bismuth or antimony oxide, about 1 to 65 weight percent of dialkyl tin maleate or dialkyl tin glutaconate and l to 95 weight percent of a polybrominated hydrocarbon, preferably a polybrominated cycloalkyl hydrocarbon.

' stantially less than is required in most of the prior art While all of the above formulations appear to have relatively good flame retardancy or flame resistance, all are subject to some other objection. For example, most of these additives must be employed in relatively large concentrations, causing adverse effects on the physical properties of the matrix polymer. In other cases, the additive must be employed in combination with antimony or a similar metal oxide which causes delustering of the polymer. Others are volatile or unstable at polymer processing temperatures, resulting in the liberation of objectionable decomposition products during processing.

It is the object of this invention to provide a flame retardant polypropylene composition which substantially overcomes the difficulties cited above. The novel flameproofing additive according to this invention is a combination of a bromophenyl ether of an aliphatic hydrocarbon and an alkyltin mercaptoester. Specifically, the invention is a flame retardant polymer composition comprising:

a. about 96 to 99.8 percent by weight of a stereoregular propylene polymer, b. about 0.1 to 2 percent by weight of a dialkyltin mercaptoester having the general formula where R,, R and R and R are the same or different alkyl groups having 1 to 18 carbon atoms and R and R are the same or different alkylene groups having 1 to 17 carbon atoms; and

c. about 0.1 to 2 percent by weight of a bromophenyl ether having the formula where R, is a saturated or unsaturated aliphatic radical having 3 to 5 carbon atoms, optionally substituted with one or more bromine atoms, y is an integer from 3 to 5 and x is an integer from 1 to 2. The preferred concentrations of the additives are about 0.25 to l percent of the mercaptoester and 0.5 to 1% of the bromophenyl ether.

It will be immediately apparent that the concentration of the additives individually and collectively is subcompositions mentioned above. Because of this, the properties of the polypropylene are altered by only a minimal amount. Tensile strength, elongation, and other properties are little different from those of polypropylene'without the additives. I

The parameter used to indicate the combustion characteristics of a polymer composition is the combustion index (C.l.). This parameter is defined as the percentage of oxygen in an oxygen-nitrogen mixture which is just sufficient to burn completely a strip of the polymer V: in. X A in. X 5 inches held inan upright position and ignited at the top, i.e.,

A CI. of at least about 22 is required in order for the flame retardancy to be adequate to pass minimum safety requirements of federal and state governments.

Polypropylene which has not been specially treated for The above listing is intended as illustrative, but not flame retardancy normally has a C.l. of about 17 to l8. limitin The compositions according to this invention measure The second group of compounds employed in the about 22 and higher as a flame-retardant compositions of this invention are al- The stereoregular propylene polymer which is employed in the compositions of this invention can be polypropylene homopolymer or a copolymer of propylene with a minor proportion, usually less than 25 weight percent, of a second olefin such as ethylene or butene-l. Such polymers are referred to by various 1 names such as isotactic polypropylene, crystalline polypropylene, stereoregular polypropylene, and the like. For the sake of convenience all such polymers are herein referred to generically as stereoregular polymers kyltin bis(alkyl-mercaptoesters). These are known additives for polymers which have been used in the past in the stabilization of poly(vinyl chloride). Exemplary of the alkyltin mercaptoesters which'can be employed are dibutyltin-S,S'-bis(n-butylmercaptopropionate),

dibutyltin-S,S-bis(n-hexylmercaptoacetate),

diethyltin-S ,S-bis( n-propylmercaptopropionate dibutyltin-S,S-bis(n-octylmercaptobutyrate), dihexyltin-S,S '-bis( n-octylmercaptovale rate of propylene dioctyltin-S,S'-bis( isooctylmercaptoacetate The brominated compounds which are employed as dioctyltins,s"bis(n'octylmercaptobutymte), flame retardants in this invention are aromaticy y p y aliphatic ethers having at least one bromophenoxy linkdioctyltin-S,S'-bis(n-butylmercaptostearate), age to an aliphatic radical and having at least three dibutyltin-S,S'-bis(n-octylmercaptolaurate). bromine substituents on each aromatic ring. Typical Th polymer d th dditive an be dry blended materials fitting this description include: and extruded into molding powder or pellets. Alternatively, they can be thoroughly melt blended as on a v Mfl 1[37 '7 m M- 7 W n paint mill or a three-roll mill followed by extrusion. The O CH2OH2CH3 additives can also be dissolved in a solvent, and the solution mixed thoroughly with the polymer and the l 3r solvent removed prior to the extrusion or other forming operation.

I i Polypropylene formulated with the flame retardant Br -OCHZCH=CHQ additives according to this invention can be employed 1|}!- in any application where polypropylene is normally employed. This includes applications such as compression Br and injection molding, extrusion into films and spinning BrO-CH1CH=CH-CH2O-@Br i or m f f I i h s invention is illustrated by the following non- Br Br limiting examples where parts and percentages are by weight unless otherwise indicated.

Br- --0cn,o1i,oinom EXAMPLES 1 to 3 E? m Polypropylene homopolymer specimens were m I prepared by blending varying amounts of l ,4-bis(2,4,6-

tribromophenoxy)-2,3-dibromo-trans-butene-2 and O(JH CII Cll' CH v% nr dibutyltin-S,S-bis(n-butylmercaptopropionate) with *f commercial isotactic polypropylene flake having an intrinsic viscosity of 2.5. The amounts of additive were Br Br chosen so as to prepare formulations containing the additive concentrat ons shown in Table 1 below. The I Br I polymer and additives were thoroughly blended in a m m Henschel mill. The compositions were then 2-roll milled for 8 minutes to effect uniform melt blending, ;1-.' following which they were compression molded into A llr' --0 (Jll -U: C--(lll V\\ llr inch plaqugg Br J i131 From each 95 inch plaque, specimens 5% in. X V4 in. X Br Br 5 inches were cut. These were employed to determine By the C.l. of the various compositions as shown in the fol- Br0 CH JCH;O-Br lowing tablellir Br Br TABLE I g 1! l s Flame Retardant Mercaptoester C.l. Control l7.8 nr--- O-CH2CH2CH2CH-CH2*O-' -m 1 l 1 224 1 2 l 0.5 21.7 Br Br ill" 3 l 0.25 22.4

EXAMPLES 4 to 12 Additional specimens were prepared by mixing dry blends of various bromophenoxy alkyl ethers and stereoregular polypropylene homopolymer with 5 per- 5 cent benzene solutions of alkyltin mercaptoesters. The where R,, R R and R are the same or different alkyl amounts were chosen to correspond to the concentragroups having 1 to 18 carbon atoms and R and R are tions shown in Table ll, below. After evaporation of the the same or different alkylene groups having 1 to 17 benzene, moldings were prepared and Cl. was detercarbon atoms; and mined as described above. The CI. values observed are 0. about 0.1 to 2 percent by weight of 1,4-bis (2,4,6- reported in Table II. tribromophenoxy)2,3-dibromo-trans-butene-2.

Tin 5E 1r C0nc., Cone, Example Flame retardant percent Mercaptoester percent 01.

4 1,4-bis(2,4,G-tribromophenoxy)-2,3-dibromo-trans- 1 Din-octyltin-S,S"bisflsooctylmereaptoacetate) r 1 butene-2.

,i V .4 0.1 Dibutyltin ,S n-hutylmcrcuptopropionate). 0.25 Dlhcxyltin'S,S-bis(n-l)utylmcrcaptoucutatu) ,7 (I .25

What I claim and desire to protect by Letters Patent 2. A composition according to claim 1 where the dialkyltin mercaptoester is dibutyltin-S,S'-bis(n-butyl- 'mercaptopropionate 3. A composition according to claim 1 where the dialkyltin mercaptoester is dioctyltin-S,S-bis(isooctylmercaptoacetate). 

1. A flame retardant polymer composition comprising: a. about 96 to 99.8 percent by weight of a stereo-regular polymer of propylene; b. about 0.1 to 2 percent by weight of dialkyltin mercaptoester having the general formula where R1, R2, R3, and R4 are the same or different alkyl groups having 1 to 18 carbon atoms and R5 and R6 are the same or different alkylene groups having 1 to 17 carbon atoms; and c. about 0.1 to 2 percent by weight of 1,4-bis (2,4,6-tribromophenoxy)-2,3-dibromo-trans-butene-2.
 2. A composition according to claim 1 where the dialkyltin mercaptoester is dibutyltin-S,S''-bis(n-butylmercaptopropionate). 